RCAIDE.Library.Methods.Aerodynamics.Common.Drag.form_drag

form_drag#

form_drag(state, settings, geometry)[source]#

Computes the form drag coefficient associated with aircraft geometry and angle of attack.

Parameters:

  • state (Data) –

    Flight conditions and aerodynamic state containing:
    • conditions.freestream.mach_numberfloat

      Freestream Mach number [unitless]

    • conditions.aerodynamics.angles.alphafloat

      Angle of attack [radians]

  • settings (dict) –

    Aerodynamic analysis settings containing:
    • supersonic.begin_drag_rise_mach_numberfloat

      Mach number at which drag rise begins [unitless]

    • supersonic.end_drag_rise_mach_numberfloat

      Mach number at which drag rise ends [unitless]

  • geometry (Data) –

    Aircraft geometry containing:
    • reference_areafloat

      Reference area for drag coefficient calculation [m²]

    • wingslist
      List of wing objects containing:
      • segmentsdict
        Dictionary of wing segments with:
        • areas.referencefloat

          Reference area of the segment [m²]

      • areas.referencefloat

        Reference area of the wing [m²]

Returns:

Results are stored in state.conditions.aerodynamics.coefficients.drag.form.total

Return type:

None

Notes

This function calculates the form drag coefficient based on angle of attack and Mach number effects. The calculation accounts for separation drag on wing segments and applies Mach number corrections for compressibility effects. The form drag is blended between subsonic and supersonic regimes using a cubic spline.

Major Assumptions

  • Form drag is primarily due to wing geometry and angle of attack

  • Separation drag follows polynomial correlation with angle of attack

  • Mach number correction is valid for typical transport aircraft

  • Vertical tail contributions are negligible

  • Cubic spline blending smooths transition between flight regimes

Theory

The Mach number correction factor is:

\(M_{correction} = 2.9788 M^3 - 6.4381 M^2 + 4.4967 M\)

where \(M\) is the freestream Mach number.

The separation drag coefficient follows a polynomial correlation:

\(C_{D,sep} = (111.41 \alpha^4 - 16.569 \alpha^3 + 1.8 \alpha^2 - 0.0242 \alpha + 0.0015) \cdot M_{correction}\)

where \(\alpha\) is the angle of attack in radians.

For wings with segments, the total form drag is:

\(C_{D,form,wing} = \sum_{i=1}^{n-1} C_{D,sep,i} \cdot S_{ref,i}\)

where \(S_{ref,i}\) is the reference area of segment \(i\).

For wings without segments:

\(C_{D,form,wing} = C_{D,sep} \cdot S_{ref,wing}\)

The total form drag coefficient is:

\(C_{D,form} = \frac{\sum C_{D,form,wing}}{S_{ref}} \cdot h_{00}(M)\)

where \(h_{00}(M)\) is the cubic spline blending function.

Definitions

‘Form Drag’

Drag component caused by pressure differences due to flow separation and body shape.

‘Separation Drag’

Additional drag caused by boundary layer separation from the surface.

‘Cubic Spline Blending’

Smooth transition function between subsonic and supersonic aerodynamic regimes.

References

[1] Empirical correlation for separation drag based on angle of attack comes from NASA CRM model [2] Unknown

See also

RCAIDE.Library.Components.Wings.Vertical_Tail, RCAIDE.Library.Methods.Utilities.Cubic_Spline_Blender